1. Field of the Invention
This invention relates to a method for the removal of hydrocarbons from soil, particularly in raising the temperature of soil containing hazardous, volatile hydrocarbons to facilitate the removal of these hydrocarbons through vapor extraction. This method is particularly well suited for the removal of hydrocarbons with relatively high boiling points and for the removal of hydrocarbons from soil containing clay or fine silt.
2. Brief Statement of the Prior Art
The improper disposal of hydrocarbons and the leakage of hydrocarbons from underground storage tanks has resulted in contamination of the ground and groundwater beneath every city and town in the developed countries of the world. Many techniques have been developed to remediate soil and groundwater contaminated with hydrocarbons. Some techniques are limited to the remediation of soil only; others remediate both the soil and the underlaying groundwater.
"Vapor extraction" is a common method of environmental remediation; this method draws vapors containing volatile hydrocarbons from the soil. As these vapors are withdrawn from the soil, the quantity of hydrocarbons remaining in the soil and the underlaying groundwater is gradually reduced. When vapor extraction is conducted long enough, the quantity of hydrocarbons remaining in the soil and groundwater are reduced to a point which is considered non-threatening to the public health. When the vapors are drawn from the soil and exhausted into the atmosphere, with or without treatment, the method is called "open-loop". When the vapors are drawn from the soil, treated, and pumped back down into the soil, the method is called "closed-loop".
Because the vapors drawn from the soil often contain hazardous hydrocarbons, local, state, or federal environmental regulations may require that the vapors be treated to prevent air pollution. When the treatment equipment generates heat, and this heat is used to heat the treated vapors prior to injecting them back into ground, the process is called "closed-loop, thermally-enhanced vapor extraction". The heated vapors slowly raise the temperature of the contaminated soil, thereby enhancing the vaporization of the remaining hydrocarbons in the soil.
"Pump and treat" is a common method of remediating contaminated groundwater only; it uses a well to extract contaminated groundwater from the ground. The extracted groundwater is treated to remove the dissolved and floating hydrocarbons before being discharged to a local sewer or surface water.
The prior art can be conveniently divided into four groups: closed-loop technologies, both thermally-enhanced (thermal) and non-thermally-enhanced (non-thermal); and open-loop technologies, both thermal and non-thermal. Techniques in these categories have been developed to simultaneously treat both soil and groundwater, groundwater only, soil only, and free (hydrocarbon) product only. They are summarized as follows: